A variety of gas barrier members have heretofore been known and, particularly, polyvinylidene chloride, polyacrylonitrile and ethylene/vinyl alcohol copolymer have been known as gas barrier resins. From the standpoint of ecological problems, however, it is a trend to refrain from using the polyvinylchloride and polyacrylonitrile. The ethylene/vinyl alcohol copolymer, on the other, has gas barrier property that greatly varies depending on the humidity, i.e., has a problem of a decrease in the gas barrier property under highly humid conditions.
In order to solve the above problems, there have been proposed a gas barrier resin composition which is obtained by reacting a polycarboxylic acid-type polymer, a crosslinking agent having 2 to 4 functional groups that react with the carboxyl groups, and metal ions of a valency of two or more so that the polycarboxylic acid polymer forms crosslinked portions due to the crosslinking agent and crosslinked portions due to the metal ions of a valency of two or more, and in which the weight ratio of the polycarboxylic acid-type polymer and the crosslinking agent is from 99.9/0.1 to 65/35 (patent document 1), and a gas barrier film obtained by forming a gas barrier coating on at least one surface of a thermoplastic resin film, the coating being formed of a polyacrylic acid that is crosslinked with a crosslinking agent containing an epoxy compound having three or more epoxy groups per a molecule thereof, and the crosslinking agent being contained in an amount of 1 to 100 parts by mass per 100 parts by mass of the polyacrylic acid (patent document 2).
The gas barrier members disclosed in the above patent documents 1 and 2 must be crosslinked to a high degree at a high temperature of not lower than 150° C. or by being heated for extended periods of time accompanied by such problems as seriously affecting the plastic base material, and lowering the productivity and consuming large amounts of energy and water since a dip treatment or a spray treatment at the time of ionic crosslinking with metal ions are necessary. Besides, the gas barrier members are not still satisfactory in regard to flexibility and retort resistance.
As a gas barrier laminated film on which dry-printing can be effected at a relatively low temperature, further, there has been proposed a gas barrier laminated film comprising a layer (a) formed from a coating solution (A) containing a polycarboxylic acid-type polymer without heat treatment and a layer (b) formed from a coating solution (B) containing a water-soluble polyvalent metal salt and an aqueous resin, the layer (a) formed from the coating solution (A) and the layer (b) formed from the coating solution (B) forming at least a pair of lamination units abutting to each other (patent document 3).